Fig 1 - uploaded by Jay E Diffendorfer
Content may be subject to copyright.
Study area. Map of southern California showing the distribution of study sites. Dark grey polygons represent urban areas. Black-outlined polygons delineate mountain ranges greater than 914.4 m (3000 ft) in elevation. Monitoring data used in our analyses comes from 61 sites. Data were collected over a sixyear period from 1995 to 2000. Sites consisted of clusters of pitfall arrays sampled three times a year for 10 days at a time. The appendix provides descriptive information for each site and covariate values. It provides sampling dates for each site.
Source publication
Detection data from a regional, reptile-monitoring program conducted by the U.S. Geological Survey were analyzed to understand the effects of urbanization and habitat composition on site occupancy of the coachwhip (Masticophis flagellum) and striped racer (M. lateralis) in coastal southern California. Likelihood-based occupancy models indicated str...
Contexts in source publication
Context 1
... of resources which likely exacerbates the effects of habitat fragmentation for species exhibiting metapopulation dynamics. The U.S. Geological Survey (USGS) has been collecting reptile-monitoring data across an area of southern California spanning ~160 Â 100 km, since the mid 1990's at 36 reserves, and on public lands, including state parks (Fig. 1, Fisher and Case, 2000). The general goal of the research is to measure the response of the reptile community to environmental stressors, including land-use change driven by urbanization. The large geographic and temporal (>5 years) scope of the data allows for comparative analysis of the responses of individual species to the ...
Context 2
... 1995 to 2000 (six field seasons), USGS collected data from 61 lower elevation (2e671 m; Appendix) sites in southern California (Fig. 1). USGS sampled herpetofauna within each site using pitfall trap arrays with three, 15 m arms of drift fence connecting seven pitfall traps and three funnel traps to capture large snakes (Fisher and Case, 2000;Fisher et al., 2008). All arrays within each site were located at least 350 m from the nearest neighboring array. The number of ...
Citations
... In Southern California, terrestrial reptiles and amphibians are a valuable group for evaluating the effects of urbanization and fragmentation because the warm, dry Mediterranean climate leads to high species richness. They are likely to experience strong effects of urban fragmentation given many species' limited dispersal abilities (e.g., Doughty and Sinervo, 1994;Nally and Brown, 2001;Anguiano and Diffendorfer, 2014;Mitrovich et al., 2018). In addition, populations isolated in urban patches are vulnerable to predation by cats and other pets (Chace and Walsh, 2006) and are often surrounded by roads which can increase mortality risks (Forman and Alexander, 1998;Koenig et al., 2001;Shepard et al., 2008;Brehme et al., 2018). ...
... In addition, populations isolated in urban patches are vulnerable to predation by cats and other pets (Chace and Walsh, 2006) and are often surrounded by roads which can increase mortality risks (Forman and Alexander, 1998;Koenig et al., 2001;Shepard et al., 2008;Brehme et al., 2018). In fact, previous studies have documented several instances of reptile and amphibian species being extirpated from patches of habitat isolated by fragmentation (Luiselli and Capizzi, 1997;Sullivan, 2000;Case and Fisher, 2001;Kjoss and Litvaitis, 2001;Fisher, 2004;Mitrovich et al., 2009Mitrovich et al., , 2018. ...
... Several habitat and anthropogenic factors may be responsible for the absence of Southern Pacific Rattlesnakes and California Striped Racers from small patches. Large-bodied wide-ranging snakes may be particularly vulnerable in small patches that are surrounded by increased vehicular traffic and introduced predators or are brush-cleared for fire safety (Zeiner et al., 1988;Luiselli and Capizzi, 1997;Kjoss and Litvaitis, 2001;Mitrovich et al., 2009Mitrovich et al., , 2018. Rattlesnakes are especially at risk due to human persecution (Mushinsky et al., 2006). ...
... Additionally, we assumed that subsequent fragmentation would not be immediately realized as changes in species occupancy but rather as shifts in abundance. These patches occurred across a gradient of sizes and isolation from the urban matrix (Fisher et al., 2002;Mitrovich et al., 2018). ...
Fragmentation within urbanized environments often leads to a loss of native species diversity; however, variation exists in responses among‐species and among‐populations within species.
We aimed to identify patterns in species biogeography in an urbanized landscape to understand anthropogenic effects on vertebrate communities and identify species that are more sensitive or resilient to landscape change.
We investigated patterns in species richness and species responses to fragmentation in southern Californian small vertebrate communities using multispecies occupancy models and determined factors associated with overall commonness and sensitivity to patch size for 45 small vertebrate species both among and within remaining non‐developed patches.
In general, smaller patches had fewer species, with amphibian species richness being particularly sensitive to patch size effects. Mammals were generally more common, occurring both in a greater proportion of patches and a higher proportion of the sites within occupied patches. Alternatively, amphibians were generally restricted to larger patches but were more ubiquitous within smaller patches when occupied. Species range size was positively correlated with how common a species was across and within patches, even when controlling for only patches that fell within a species' range. We found sensitivity to patch size was greater for more fecund species and depended on where the patch occurred within a species' range. While all taxa were more likely to occur in patches in the warmer portions of their ranges, amphibians and mammals were more sensitive to fragmentation in these warmer areas as compared to the rest of their ranges. Similarly, amphibians occurred at a smaller proportion of sites within patches in drier portions of their ranges. Mammals occurred at a higher proportion of sites that were also in drier portions of their range while reptiles did not differ in their sensitivity to patch size by range position.
We demonstrate that taxonomy, life history, range size and range position can predict commonness and sensitivity of species across this highly fragmented yet biodiverse landscape. The impacts of fragmentation on species communities within an urban landscape depend on scale, with differences emerging among and within species and populations.
... Without a clear understanding of where and when sea snakes are active, and the abiotic and biotic factors that drive those patterns, it will be very difficult to tease apart potential causation for cases of population collapse. Understanding the drivers of habitat utilisation has proved to be helpful in addressing conservation issues in terrestrial snakes 14,37 , but our lack of knowledge about marine snakes curtails our ability to extend those insights to oceanic systems. ...
Tidal cycles are known to affect the ecology of many marine animals, but logistical obstacles have discouraged behavioural studies on sea snakes in the wild. Here, we analyse a large dataset (1,445 observations of 126 individuals) to explore tidally-driven shifts in the behaviour of free-ranging turtle-headed sea snakes (Emydocephalus annulatus, Hydrophiinae) in the Baie des Citrons, New Caledonia. Snakes tended to move into newly-inundated areas with the rising tide, and became more active (e.g. switched from inactivity to mate-searching and courting) as water levels rose. However, the relative use of alternative habitat types was largely unaffected by tidal phase.
... A reptile and amphibian monitoring program is one of many MEDN monitoring programs, and is of high interest due to population declines associated with anthropogenic (e.g., urban development and exotic species) and environmental stressors (e.g., temperature extremes, drought, ultraviolet radiation; Blaustein & Wake, 1990, Fisher, Suarez, & Case, 2002, Delaney, Riley, & Fisher, 2010, Sinervo et al., 2010, Mitrovich, Diffendorfer, Brehme, & Fisher, 2018. Of particular concern is reptile and amphibian persistence at Cabrillo National Monument, and more generally at the Point Loma Ecological Conservation Area (PLECA) of which Cabrillo is part (Figure 1). ...
... Of these, the snake is too rare for quantitative analysis, one of the lizards is in decline, and two of the remaining lizard species are not growing as large. Additional work is needed to determine the taxonomic breadth of these trends at PLECA, and which of a host of potential ecological threats (spread of invasive species, changing weather patterns, light pollution, declines in arthropod abundance, loss of genetic diversity, increased human usage, etc.) are contributing to local loss of biodiversity Menke, Holway, Fisher, & Jetz, 2009;Mitrovich et al., 2018;Perry, Buchanan, Fisher, Salmon, & Wise, 2008;Perry & Fisher, 2006). ...
Long‐term ecological monitoring provides valuable and objective scientific information to inform management and decision‐making. In this article, we analyze 22 years of herpetofauna monitoring data from the Point Loma Ecological Conservation Area (PLECA), an insular urban reserve near San Diego, CA. Our analysis showed that counts of individuals for one of the four most common terrestrial vertebrates declined, whereas counts for other common species increased or remained stable. Two species exhibited declines in adult body length, whereas biomass pooled over the five most common species increased over time and was associated with higher wet season precipitation. Although the habitat and vegetation at PLECA have remained protected and intact, we suspect that changes in arthropod communities may be driving changes in the abundance, growth, and development of insectivorous lizards. This study underscores the value of long‐term monitoring for establishing quantitative baselines to assess biological changes that would otherwise go undetected. Species‐specific capture rate patterns for adults and juveniles over a calendar year. The x‐axis is the month (1 = January, …, 12 = December) and the y‐axis is capture rate (captures in month i/array‐nights in month i). Monthly captures were the monthly count data pooled over the years 1995–2016; monthly array‐nights were from Table S2.
Conservation and management of drylands is a global challenge. Key attributes of these ecosystems, such as dominant vegetation including shrubs, can provide a crucial mechanism to inform conservation strategies. The shrub species Ephedra californica and Larrea tridentata are common native shrub species within the deserts of California and frequently benefit other plant and animal species. Here, we tested the hypothesis that shrubs support reptile and amphibian communities through relative increases in available habitat, estimated through increasing shrub densities at the site level. Reported occurrence data from the Global Biodiversity Information Facility (GBIF) and high-resolution satellite images were used to test for local-to-regional patterns in reptile and amphibian distribution and diversity by shrub densities at sites. At 43 distinct sites, the relationship between shrub density and reported reptile and amphibian communities was also tested. A total of 71 reptile and amphibian species were reported regionally. Increases in shrub density across sites positively influenced the relative abundance and richness of reptiles and amphibians observed. Moreover, increasing shrub density also had a positive influence on species evenness. Aridity differences between sites did not significantly influence the relationship between shrub density and reptiles and amphibians suggesting that the relationship was robust. This study highlights the importance of foundational shrub species in supporting reptile and amphibian communities in arid and semi-arid regions. Large-scale patterns of biodiversity in deserts can be supported by positive plant-animal interactions including small islands of fertility and resources for animals in the context of a warming climate.
Extensive urbanization in coastal southern California has reduced natural habitat in this biodiversity hotspot. To better conserve ecological communities, state and federal agencies, along with local jurisdictions and private stakeholders, developed regional conservation plans for southern California. Although many protected areas exist within this region, the patchwork nature of these protected areas might not provide good coverage for species that require multiple habitat components, such as amphibians with complex life histories. Because of declines in the past century, the status of the western spadefoot (Spea hammondii) in southern California is of concern to state and federal wildlife agencies. Species distribution models (SDMs) can aid in determining the conservation status of imperiled species by projecting where suitable habitat remains and how much is protected from further development. We built SDMs that integrated site-occupancy data from systematic pitfall trapping surveys and presence-only data from biodiversity databases and citizen science platforms to project the current distribution of western spadefoots in southern California. Western spadefoot occurrence was positively related to the cover of grassland or shrub/scrub and the % sand in the soil within a 1000 m buffer, and was negatively related to slope, elevation, and distance to ephemeral streams or vernal pools. Most of the remaining unprotected habitat for western spadefoots is in the southern half of its historical range in western San Diego and Riverside counties. A few large tracts of spadefoot habitat exist on U.S. Department of Defense lands and smaller tracts remain on ecological reserves owned by state and local government agencies. Only small patches of habitat remain in the northern half of this clade’s historical range in Ventura, Orange, Los Angeles, and San Bernardino counties. Existing regional conservation plans provide ostensible spatial coverage of the majority of extant habitat for western spadefoots in southern California, but most of the habitat within the jurisdiction of these plans lacks formal protection, exposing this species to further declines as urbanization continues in the 21st century.
Conspecific animals living in multiple habitats may utilize different behaviours to survive and thrive in their environments. The Pacific rattlesnake (Crotalus oreganus), a generalist pit viper species, lives in a myriad of habitat types. We hypothesized that populations inhabiting hot, inland habitats and those in cool, coastal habitats would exhibit different behavioural strategies, especially those related to thermoregulation. Additionally, we determined whether environmental factors could be used as predictors of certain behaviours. We recorded environmental and behavioural data while radio-tracking adult, male rattlesnakes from two inland sites and two coastal sites throughout their active season. We found significant differences in thermoregulatory behaviour, with coastal snakes found more frequently above ground and in an active state than inland snakes. Additionally, wind, cloud cover, and air temperature were significant predictors of several snake behaviours. These results suggest that rattlesnakes exhibit plasticity in thermoregulatory behaviour.
Ecologists endeavour to develop survey techniques that are cost-effective for the species they target and robust enough for statistical analysis. Using time as a measure of effort, we compared visual encounter surveys with artificial cover objects (strapped to trees), targeting an arboreal elapid, the pale-headed snake (Hoplocephalus bitorquatus) and its potential prey (geckos). Within a red gum forest vegetation community with relatively high snake density, capture rates were 0.6 ± 0.1 (s.e.) snakes/person-hour using visual encounter surveys, compared with only 0.1 ± 0.1 snakes/person-hour using cover objects. The probability of detection of pale-headed snakes was estimated from occupancy modelling at 0.70 ± 0.06 in visual encounter surveys and 0.19 ± 0.09 in cover object surveys. Gecko capture rates (among all vegetation communities) were significantly greater (P < 0.001) using cover objects. The probability of detection of geckos was estimated from occupancy modelling at 0.77 ± 0.05 in visual encounter surveys and 0.97 ± 0.02 in cover object surveys. Geckos favoured (P < 0.001) cover objects facing south during all seasons except winter. Artificial cover objects may provide some value in detecting pale-headed snakes in vegetation communities where habitat resources are limited; however, where resources are plentiful, visual encounter surveys are likely to remain the most cost-effective survey option.
